The Science Journal of the American Association for Respiratory Care

1995 OPEN FORUM Abstracts

The Effect of Actuation Interval on Dose Availability with Metered Dose Albuterol

J. L. Rau, Ph.D., RRT, Georgia State University, Ruben D. Restrepo, M.D., RRT, Egleston Children's Hospital of Emory University, Atlanta, GA.

The usual instructions with metered dose inhalers (MDI) suggest a pause time of 30 seconds between actuations to allow adequate refill of the metering valve. Purpose: This study examined the effect of decreasing interval times between MDI actuations with albuterol (Proventil, Schering) on delivered dose from the actuator mouthpiece.

Methods: A sample of six unused MDI canisters of albuterol were selected and weighed to ensure comparable fullness. Each MDI was shaken and four actuations wasted prior to dose measurements. A Gelman Versapor 0.45 micron, 25 mm filter was fitted over the MDI mouthpiece of the actuator using a one inch flexible plastic holder. Each MDI was then discharged twice, at time intervals of 2, 3, 5, 10, 15, 20, 25 and 30 seconds. The filters were washed with 5 ml of ethanol, and the resulting drug solution analyzed by spectrophotometer at 278 nm. Drug dose was calculated by simple proportion, using a standard solution of albuterol of known concentration.

Results: Mean dose and standard deviations are given, in micrograms:

Interval, seconds

23510 15 20 25 30

xbar 185.8 192.5 192.7 185.3 191.9 186.7 188.0 187.6

SD:8.6 13.18.4 7.7 10.410.68.0 9.9

There was no significant difference among the intervals using a randomized block, repeated measures analysis of variance (p=.19). Conclusion: Two actuations of MDI albuterol at intervals as short as two seconds does not result in abnormal doses. These results do not indicate the possible effect on lung distribution with rapid sequential MDI actuations.


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